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Other Crest Power Amps

Discussion in 'Amps and Cabs [BG]' started by Piezoman, Dec 25, 2005.


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  1. Piezoman

    Piezoman

    Nov 29, 2002
    Bronx, New York
    Looking over the CA-9 vs. plx 3402 thread got me interested in crest poweramps and seeing as how they seem to be of such a higher quality, how does the rest of their line compare to the CA-9?

    Are the CA series amps the best they have to offer in terms of efficency and clarity? There are other lighter wieght models with similair if not more powerful outputs. Is crest better or is it just the CA series?
     
  2. Whoa there buddy "seeing as how they seem to be of such a higher quality" is hardly the right phrase to use :smug:

    Both PLXs and CA-9s are top notch amps.
     
  3. Horny Toad

    Horny Toad Guest

    Mar 4, 2005
    NJ

    I'm the guy who started that thread, and I agree with Fretless5verfan. The PLX series is every bit the equal of the CA9 in terms of fit, finish, build quality. It is superior in terms of features, such as Speakon outputs and filtering options. It is in the area of sound that I feel the CA9 is better. Better for me.

    I owned two PLX's, a 2402 and 3402. I can't say one bad thing about them. There's no reason to. After trying my recently acquired CA9, I feel I've found an amp that works better for me. The whole "sounds better" thing is totally subjective, and I'll be the first to admit that.


    [​IMG]
     
  4. Ostinato

    Ostinato Guest

    Feb 7, 2005
    Toronto ON
    I've got a Crest ST1500. It's a switching amp very similar to the PLX, similar in weight anyway. Crest and QSC both have a great reputation and good customer service. I bought the Crest because their distributer is located in my area. Great sounding amp.
     
  5. Piezoman

    Piezoman

    Nov 29, 2002
    Bronx, New York
    I meant in terms of sound quality. Forgot to specify.

    So.....other crests???
     
  6. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    i'm using a good old crest fa-901...bridged i get 800 chest slammin' watts continuous at 4 ohms. i was considering a ca series, which i've owned before, but when this came along in a case for 200 bucks (looks new, btw) i jumped on it. same tight, thick bass as the ca i owned, same clarity, just not as much power per pound (it weighs in at 35lbs.). the fan is a hair louder than the ca series, but not enough to notice at a gig.
    great amp!
    doug
     
  7. Piezoman

    Piezoman

    Nov 29, 2002
    Bronx, New York
    So that thick bass should be present throughout their line? Even the lighter models?
     
  8. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    it depends on a few factors...i wouldn't use less power than in the 901.
    it's an older model, so it's heavier. the sound/ components debate is a massive can of worms i don't want to open, but my feelings are obvious with my choice of amp. i like large transformers and reserve power. a couple other factors in the bass response is also due to slew rate and damping factor. search it, you'll find alot of info.
    and a quick pic of the 901:
    [​IMG]
    cheers
    doug
     
  9. Haven't encountered any of the lighter Crests but the old '001 series will leave a CA9 for dead. There's a reason that they were one of the top touring amplifiers for years.. I've heard good things about the Pro 200 series too. We had a bunch of CA9s go down a few years ago and Crest was excellent to deal with on the matter. Good service form them.
     
  10. i have a pro 200, but...

    i have not done any comparisons with it against any PLX amps.

    i bought it from crest when i worked there.

    i like its sounds, but i also liked the employee price i got, and the weight of it. i have compared it to a crest CC1800, and it was considerably tighter and louder, but less aggressive in the midrange than the CC1800. if you have the coin for it, it's well worth the money.

    just to clarify, though, the ST1500 is class D; the PLX series are class AB, and then class H for the higher powered amps. both have a switch-mode power supply (SMPS). the LT series from crest have the same class D output stage as the ST series, but a low frequency power supply.

    robb.
     
  11. notrt

    notrt

    Jun 29, 2004
    Afternoon to all: I currently have 2 FA-901's and one FA-2401 up at the Church where I play. The '901's used to be in my secular band's amp rack; one for me, one for the mains...they're now in the Church's amp rack pushing the mains and monitors.

    The '2401 used to belong to my teacher, Jim Charleson, and currently pushes a good deal of the ambient sound turned out by my "big rig" up at Church. One way or another, I've been using these for over 15 years; only had to replace one capacitor in one of the '901's in all of that time. I think they're pretty stalwart performers.

    :bag: Having just said that, as much as I hate to say this, I do not think the FA-series are in the same league as the CA series...here's "why", at least as I perceived it...when pushed hard with a lot of bass content, the level (and quality---clarity, definition and punch...) of the sound I'd hear would seem to deteriorate, or "sag", but would quickly recover (less than a minute or so...) if they had any breathing room. I.M.H.O., the CA doesn't seem to do that. :bag:

    As I noted above, this is simply my take on it; nothing more or less than that.

    later...

    RC
     
  12. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    curious, was that under the same power conditions?
    sounds like a brownout.... i have yet had the need to max the amp,
    i run it about 3/4 for a loud rock gig, no noticeable sag for me in tone or power...i'll dime it next time and see what happens....
    d

    just wanted to add, i did open up the amp and blow it out...
    both ca and fa series can get quite mucked up fairly quickly,
    and this can cause thermal problems....notrt, did you ever try cleaning out your amps?
     
  13. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Slew rate and damping factor are the two most overrated specs in the marketing of power amplification. They're tailor-made to impress noobs and uninformed buyers.

    Slew rate is the fastest rate of change in the output voltage that the amp can produce. Without knowing the amp's maximum output voltage swing and the highest signal frequency the amp needs to reproduce, it is useless by itself. Slew rate isn't even an issue for bass.

    Some amps are marketed as "more slew rate=better." But in actuality, any competently designed power amp has some low-pass filtering--typically anywhere from 50 kHz to 200 kHz--to reduce the amp's sensitivity to RF noise. This allows smooth operation of the amp even if there is a high-power AM radio station or an aviation navigation aid nearby. This low-pass filtering limits the slew rate of the amp. You can be sure that an amp with a slew rate that is really high compared to its maximum output voltage would be a likely candidate to have problems in RF-heavy environments.

    I doubt that there is a power amp on the market from any reputable company that has a deficient slew rate. You can even calculate how much slew rate is necessary for a power amp.

    Let's say you have an amp rated at 500 watts into 8 ohms. That would be a maximum RMS output voltage of 63.2 volts, and a maximum peak voltage of 89.4 volts.

    The slew rate in volts per second would be
    Vpk * 2PI * F
    so a full power signal at 20 kHz would have a maximum rate of change of 11 million volts per second. Scaled down to the more familiar volts per microsecond, that works out to 11 volts per microsecond. Most power amps of that magnitude would have slew rates at least around double that.

    The bottom line with slew rate: don't worry about it.

    Damping factor is a marketing-friendly way of stating an amp's output impedance. It is marketing-friendly in that it magnifies insignificant differences in output impedance into massive numerical disparities that look impressive on paper. For example, an amp with an output Z of 0.03 ohm driving an 8-ohm load has a damping factor of 267, while on with an output Z of 0.01 ohm has a damping factor of 800. Twenty milliohms is not a big difference, yet the numbers derived from that difference are wildly disparate.

    But wait, there's more! Why don't manufacturers just have as low an output impedance as possible, as close to zero ohms as they can get? First, zero resistance is impossibe, but even with plain wire you can get pretty close. Second, and more important, is that a competently designed power amp has an output network on it to help ensure the circuit's stability and to decouple RF noise picked up by the speaker cabling (also known as an antenna in the RF realm) to help keep it out of the amp circuitry. An amp without such an output network would have really big numbers to print on the spec sheet, but it would probably have some real reliability issues.

    The output network's impedance will typically be a little higher at high frequencies and extremely low at lower frequencies. Therefore, the frequency range measured will have a big effect on the damping factor spec. The IHF damping factor method, which QSC and some, but not all, other manufacturers use, covers up to 1 kHz. If measured at only up to 400 Hz, the same amps specified by an IHF damping factor spec would have much larger DF numbers. And even bigger if DF was measured at up to only 100 Hz. In this case, what the spec sheet doesn't tell you could mean much more than what it does.

    And then there is the influence of speaker cabling. Two and a half feet of two-conductor 16-gauge copper wire--not a bad choice for speaker cabling--would have a resistance of 20 milliohms. That was enough in an example above to cause a change in damping factor from 800 to 267. Even if the amp's damping factor was infinity, that wire alone would bring the net damping factor down to 400.

    Like slew rate, I doubt that there is a solid state power amp from any reputable brand that has a damping factor that is actually too low to be useful for bass.

    The bottom line with damping factor: got a couple hundred or better? Use adequate speaker cables and don't worry about it.
     
  14. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    The FA series is definitely more of a budget line than the CA series, and the LA series was an entry-level series compared to the FA. Both LA and FA used a hybrid IC to drive the output modules. The CA series is based on the old Professional series (which was made with mostly discrete components), scaled down to lower price points. (When I was there I wrote various revisions or originals of the FA, LA, and Pro Series owner's manuals.) All are or were very accurate amps, as power amps should be.
     
  15. Bob, you officially know too much :p

    Seriously though, those were some very informative posts for someone like me who doesn't know a ton about amps. Thanks :D
     
  16. Horny Toad

    Horny Toad Guest

    Mar 4, 2005
    NJ

    Bob has always been extremely informative about QSC amps, and amps in general. Never would I question his knowledge in this area.

    All the numbers, stats, science and logic in the world cannot change that which is most important - what you hear. These are always interesting discussions, but for me, there are three words that sum it all up:

    Trust
    Your
    Ears

    :D



    [​IMG]
     



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